South African Journal of Chemistry - Volume 57, Issue 1, 2004
Volumes & issues
Volume 57, Issue 1, 2004
Simple and Effective Procedure for Immobilization of Oxidases onto MnO2-bulk-modified, Screen-printed Carbon ElectrodesSource: South African Journal of Chemistry 57, pp 1 –7 (2004)More Less
Nafion<sup>(R)</sup> film entrapment of oxidases onto the surface of MnO<sub>2</sub>-(5%, m:m) bulk-modified, screen-printed carbon electrodes was studied taking the inexpensive glucose oxidase as a model enzyme. The Nafion<sup>(R)</sup>-enzyme film was formed by drop-coating the suspension onto the surface of the electrode. Comparisons weremadeamong biosensors developed by using as-received, neutralized, and diluted (to 1% in methanol, ethanol or phosphate buffer) Nafion<sup>(R)</sup> in a flow injection (FI) mode. The amperometric response to injections of standard glucose solution was the highest for biosensors produced using neutralized Nafion<sup>(R)</sup>. The effect of enzyme load per electrode (10-1190 <SPAN lang=AF style="FONT-FAMILY: Symbol; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-char-type: symbol; mso-symbol-font-family: Symbol"><SPAN style="mso-char-type: symbol; mso-symbol-font: Symbol">m</SPAN></SPAN>g) was investigated and 50 <SPAN lang=AF style="FONT-FAMILY: Symbol; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-char-type: symbol; mso-symbol-font-family: Symbol"><SPAN style="mso-char-type: symbol; mso-symbol-font: Symbol">m</SPAN></SPAN>g enzyme in the film per electrode was found to produce very good sensitivity as well as to be economical. Good reproducibility was achieved for three different biosensors (RSD of the means = 5.7%). The operational parameters for the glucose biosensor produced with this immobilization procedure were assessed and figures of merit obtained at the selected parameters. It has been observed that the effect of Nafion<sup>(R)</sup> to repel interfering ions like ascorbate and urate was lacking in this system. A preliminary investigation incorporating a hydrogen peroxide permselective membrane layer prior to enzyme immobilization gave promising result with polyurethane.
Chromium Speciation Analysis by Ion Chromatography Coupled with Inductively Coupled Plasma - Optical Emission SpectroscopySource: South African Journal of Chemistry 57, pp 8 –14 (2004)More Less
Two methods coupling ion chromatography with inductively coupled plasma - optical emission spectroscopy (ICP-OES) were developed for the simultaneous separation and determination of Cr(III) and Cr(VI) species. In the first method, anion chromatography with sodium bicarbonate/carbonate solution as the eluent was utilized. Cr(III) species were protected from precipitation by complexation with ethylenediaminetetra-acetic acid (EDTA) prior to analysis. The detection limits were determined experimentally as 0.05 mg L<sup>-1</sup> for both species. Most of the common cations were found to interfere with the accurate determination of Cr(III) when present in excess of 50 mg L<sup>-1</sup>. In the second method using cation chromatography, a guard column was employed in conjunction with a stepwise elution programme to elute the chromium species. The detection limits were experimentally determined as 0.1 mg L<sup>-1</sup> for both species.
Study on Colour Reaction of Vanadium(V) with 2-(2-Quinolylazo)-5-Diethylaminophenol and Its ApplicationSource: South African Journal of Chemistry 57, pp 15 –18 (2004)More Less
A sensitive, selective and rapid method has been developed for the determination of vanadium based on the rapid reaction of vanadium(V) with 2-(2-quinolylazo)-5-diethylaminophenol (QADEAP). The QADEAP reacts with V(V) in the presence of citric acid-sodium hydroxide buffer solution (pH =3.5) and cetyl trimethylammonium bromide (CTMAB) medium to form a violet chelate of a molar ratio 1:2 (V(V) to QADEAP). The molar absorptivity of the chelate is 1.23 x 10<sup>5</sup> L mol<sup>-1</sup> cm<sup>-1</sup> at 590 nm in the measured solution. Beer's law is obeyed in the range of 0.01~0.6 <SPAN lang=AF style="FONT-FAMILY: Symbol; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-char-type: symbol; mso-symbol-font-family: Symbol"><SPAN style="mso-char-type: symbol; mso-symbol-font: Symbol">m</SPAN></SPAN>g mL<sup>-1</sup>. This method was applied to the determination of vanadium(v) with good results.
An Investigation into the Use of Microchemistry Experiments in First-year University-level PracticalsSource: South African Journal of Chemistry 57, pp 19 –23 (2004)More Less
In the case study reported on in this article the desirability to convert first-year university-level practicals in chemistry from conventional techniques to microscale methods was investigated. The results indicated that microscale experiments did not result in a noticeable saving in time and gave results that compare favourably with those of the conventional experiments. The most positive aspect of microscale experiments is a long-term financial one. A few negative aspects of microscale experiments were identified in the study.
In hierdie bydrae word 'n gevallestudie gerapporteer oor die wenslikheid om eerstevlak universiteitschemie-prakties van konvensionele tegnieke na mikroskaaltegnieke om te skakel. Die resultate toon dat die mikroskaaleksperimente nie noemenswaardig tydsbesparend is nie en resultate lewer wat goed vergelyk met dié van konvensionele eksperimente. Die mees positiewe aspek van mikroskaaleksperimente is finansiële besparing op die lang termyn. Enkele negatiewe aspekte van mikroskaaleksperimente is in die ondersoek geïdentifiseer.
Quantification of Sugars in Soft Drinks and Fruit Juices by Density, Refractometry, Infrared Spectroscopy and Statistical MethodsSource: South African Journal of Chemistry 57, pp 24 –27 (2004)More Less
The amount of sugar in soft drinks and fruit juices has been quantified by density, refractometric and infrared spectroscopic methods. Density and refractometric methods can be used to obtain only the total amount of sugar. However, infrared spectroscopy distinguishes itself as a fast and reliable method for quantitative analysis. Fourier-transformedspectroscopy in combination with a mathematical treatment of the spectra of samples allows the amount of different sugars such as glucose, fructose and sucrose to be determined.
The Synthesis of QADMAA and its Application to the Solid Phase Extraction and Spectrophotometric Determination of CobaltSource: South African Journal of Chemistry 57, pp 28 –32 (2004)More Less
In this paper, the synthesis of a new chromogenic reagent, 2-(2-quinolylazo)-5-dimethylaminoaniline (QADMAA), is reported. A sensitive, selective and rapid method for the determination of cobalt based on the rapid reaction of cobalt(II) with QADMAA and the solid phase extraction of the Co(II)-QADMAAchelate withC<sub>18</sub> membrane disks was developed. In the presence of a pH=5.5 buffer solution and a cetyl trimethylammonium bromide (CTMAB) medium, QADMAA reacts with cobalt to form a violet complex with a molar ratio of 1:2 (cobalt to QADMAA). This chelate was enriched by solid phase extraction with C<sub>18</sub> membrane disks and an enrichment factor of 50 was obtained. The molar absorptivity of the chelate is 1.32x10<sup>5</sup> L mol<sup>-1</sup> cm<sup>-1</sup> at 616 nm in the measured solution. Beer's law is obeyed in the range of 0.01~0.6 <span style='font-family:Graeca'>m<o:p></o:p></span>g mL<sup>-1</sup>. The relative standard deviation for eleven replicate sample at the 0.01 <span style='font-family:Graeca'>m<o:p></o:p></span>g mL<sup>-1</sup> level is 1.35%. The detection limit reached 0.02 <span style='font-family:Graeca'>m<o:p></o:p></span>g L<sup>-1</sup> in the original samples. This method was applied with good results to the determination of cobalt in environmental samples.
Spectrophotometric Studies of the Behaviour of Multidentate Schiff Base Ligands with Copper(II) in Methanol SolutionSource: South African Journal of Chemistry 57, pp 33 –36 (2004)More Less
Four formation reaction complexes of polydentate Schiff base ligands derived from condensation of ethylenediamine with salicylaldehyde (L<sub>1</sub>) and 2-pyridinecarboxaldehyde (L<sub>2</sub>) and of diethylenetriamine with salicylaldehyde (L<sub>3</sub>) and 2-hydroxy-1-naphthaldehyde (L<sub>4</sub>) as electron donors with copper (II) chloride as an electron acceptor in methanol were studied spectrophotometrically at 301 K. The absorption band wavelengths of the electron donors, the electron acceptor and their complexes were measured and studied. Parameters such as the molar absorptivities, <span style='font-size:11.0pt;mso-bidi-font-size:10.0pt;font-family:Graeca'>e</span><sup>AD</sup>, of these complexes and the equilibrium constants, K<sup>AD</sup>, of their formation reactions obtained from the Benesi-Hildebrand equation were established and discussed. The absorption band energies of the complexes, E, the ionization potentials of the Schiff base ligands, I<sup>D</sup>, and the Gibbs energy changes of the above reactions, ∆G, were calculated. Finally, kinetic parameters such as the orders of the reactions, and the rate constants of the forward and reverse reactions, k<sub>1</sub> and k<sub>-1</sub>, were determined.
The Dependence of 1J(C, H) and 3J(C, H) on a Nitrogen Lone-pair and Carbonyl Group. Application to DiazepamSource: South African Journal of Chemistry 57, pp 37 –39 (2004)More Less
The relatively large difference in the directly bonded (C, H) coupling constants of the C(3) methylene group in diazepam can be attributed to the spatial relationship of the C(3)-H bonds and the C(2)=O group and N(4)-lone pair. INDO-FTP calculated <sup>1</sup>J(C-3, H) values reveal a linear relationship with the C(2)-C(3)-N(4)-C(5) dihedral angle, a non-linear relationship with the C-H bond length and small negative change depending on the N(1)-C(2)-C(3)-N(4) dihedral angle. The INDO-FTP calculated <sup>3</sup>J(C-5, H) values depend on the corresponding dihedral angle and the spatial relationships of the C=N double bond and the aryl group.
Synthesis of TOPO-capped Nanocrystals of Copper Sulphide from a Single-source Precursor, [Cu(S2CNMe(nHex))2]Source: South African Journal of Chemistry 57, pp 40 –43 (2004)More Less
Nearly mono-dispersed TOPO-capped copper sulphide nanocrystals of <I>ca.</I> 4.5 nm (diameter) have been synthesized from [Cu(S<sub>2</sub>CNMe(<sup>n</sup>Hex))<sub>2</sub>]. The absorption spectrum of the (Cu<sub>2</sub>S) nanoparticles shows a large blue shift (2.09 eV) in relation to bulk Cu2S (1022 nm, 1.21 eV). The PL gives a broad spectrum with an emission maximum at 477 nm. The HRTEM of the nanoparticles shows clusters of particles on the copper grid with clear lattice fringes.
Investigation of the Solvent Enclathration Potentials of 5-Phenyl-10, 11-dihydro-5H-dibenzo[a,d]cyclohepten-5-ol and Related Seven-membered Ring AlcoholsSource: South African Journal of Chemistry 57, pp 44 –48 (2004)More Less
Four previously reported tricyclic alcohols containing seven-membered central B-rings, 5-phenyl-10, 11-dihydro-5<I>H</I>dibenzo [<I>a,d</I>]cyclohepten-5-ol, 5-phenyl-5<I>H</I>-dibenzo[<I>a,d</I>]cyclohepten-5-ol, 11-phenyl-6, 11-dihydrodibenzo[<I>b,e</I>]oxepin-11-ol and 11-phenyl-6, 11-dihydrodibenzo[<I>b,e</I>]thiepin-11-ol have been synthesized and their solvent enclathration (inclusion) properties investigated and compared by using <sup>1</sup>H-NMR and differential scanning calorimetry (DSC). The presence of an oxygen or a sulphur atom, respectively, in the B-ring of the latter two compounds had a detrimental effect on the solvent enclathration properties of the host compounds as compared to those containing an ethane or ethylene bridge. This suggests that, although enclathration is highly dependent on the hydrogen bonding ability of the host, rigidity of the structure plays a crucial role in the formation and stability of these complexes.
Effect of Calcination and Reduction Temperatures on the Reduction and Activity of Boron-modified Co/TiO2 Fischer-Tropsch CatalystSource: South African Journal of Chemistry 57, pp 49 –52 (2004)More Less
The effect of calcination and reduction temperatures on the reducibility, dispersion and Fischer-Tropsch activity of 10 wt% cobalt supported on titania catalyst modified by 0.1 wt% boron has been studied. The percentage reduction and percentage dispersion were found to decrease with increasing calcination temperature. The higher calcination temperatures decreased the total CO hydrogenation activity, but did not affect the turnover frequency. The decrease in CO hydrogenation rate with increasing calcination temperature is attributed to a decrease in the number of surface active sites. The higher reduction temperature also decreased the total activity. This may be due to the loss of the surface active sites, caused by blocking of the TiO<sub><SPAN lang=AF style="FONT-FAMILY: Symbol; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-char-type: symbol; mso-symbol-font-family: Symbol"><SPAN style="mso-char-type: symbol; mso-symbol-font: Symbol">c</SPAN></SPAN></sub> phases produced at higher reduction temperatures. The higher calcination temperature shifted the F-T product spectrum to the lower weight hydrocarbons. The reduction temperature did not affect the product selectivity.
Kinetic Aspects of the Direct Electrochemical Oxidation of p-Xylene in Methanol using Graphite ElectrodesSource: South African Journal of Chemistry 57, pp 53 –56 (2004)More Less
The kinetics of the electrochemical oxidation of <I>p</I>-xylene (A) in methanol solutions containing tetraethylammonium p-toluene sulphonate as supporting electrolyte using graphite electrodes were investigated. It was shown that <I>p</I>-xylene is first oxidized to the intermediate 4-methylbenzyl methyl ether (B), which is then further oxidized to the corresponding acetal, 4-methyl benzaldehyde dimethyl acetal (C). The stepwise reaction A->B->C was first tested for first order consecutive kinetics and this approach was shown to be invalid. A model based on parallel consecutive second order kinetics was then proposed in which solvent participation assists in the electrochemical oxidation of the substrate, through free radical reactions. Using the ratios of the relevant k values, instead of their absolute values, the concentrations of each reactant are expressed as ratios with respect to the initial concentration of A. These are calculated using expressions based on the fraction of A remaining at a particular time. It is shown that the calculated curves agree well with those based on the observed values, indicating that the proposed kinetic model is acceptable.